Run time meter installation for microwave ovens

ABSTRACT

A microwave oven for rental installations is provided with a run time meter which cumulatively records the periods of time during which the oven is in operation. The run time meter is hidden behind a grille at the front of the oven, the grille being removable for access to the meter upon removal of a hidden Allen headed screw.

llnited States Patent Foerstner 1 May 22, 1973 54] RUN TlME METER INSTALLATION 1,505,198 8/1924 Hough ..58/145 R FOR MICROWAVE OVENS 3,418,802 12/1968 Little et a1. ..58/145 R [75] Inventor: George C. Foerstner, Amana, Iowa Primary Examiner v. Truhe [73] Assignee: Amana Refrigeration, Inc., Amana, Assistant Examiner-Hugh D. Jaeger Iowa Attorney- Haven E. Simmons and James C.

221 Filed: Sept. 20, 1971 Nemmers [21] Appl. No.: 182,019 ABSTRACT A microwave oven for rental installations is provided [52] US. Cl. ..2l9/10.55, 58/145 R wi h a r n im m ter which cumulatively records the [51] Int. Cl. ..G04b 5/20, l-l05b 9/06 p riods f ime during which the oven is in operation. [58] Field of Search ..2l9/ 10.55; 58/39.5, The run ti e er is h dden behind a grille at the 58/ 145 R front of the oven, the grille being removable for access to the meter upon removal of a hidden Allen headed [56] References Cited screw.

UNITED STATES PATENTS 1 Claim, 4 Drawing Figures 3,339,054 8/1967 Deaton ..2l9/l0.55

I80 RT M 3 w r 1 1 I20 ,1 I 8b I I 3 l9 EL 19a PATENIDMY22|915 SHEET 1 OF 2 FIG I GEORGE C. FOERSTNER ATTORNEY PATENTEL 2 9 3 SHiET 2 OF 2 FIG 4 INVENTOR.

GEORGE C. FOERSTNER BY ATTORNEY RUN TIME METER INSTALLATION FOR MICROWAVE OVENS BACKGROUND OF THE INVENTION Large, commercial microwave ovens have long been in use. Much more recently, however, small, countertop microwave ovens have appeared on the market for domestic use in homes. From the latter has evolved a line of heavier duty, countertop ovens for use in small restaurants and in connection with food vending apparatus. The latter apparatus is often rented, and the plan is to make the heavier duty countertop ovens available to restaurants and to food vending operators also on a rental basis. Since in these situations it is more satisfactory all around to tie the amount of the rentals to the amount of oven usage, some method of determining and recording the latter is required. At the same time, whatever the method used for that purpose, the mechanism involved should not be readily visible or accessible to the lessee. Instead, it should be relatively hidden and difficult of access to all but the lessor or his servicemen. The object of the present invention is to provide such an arrangement for microwave ovens for installations of the types concerned.

SUMMARY OF THE INVENTION An electrically driven run time meter is placed behind a grille and filter in the air inlet at the front of the oven. One edge of the grille is placed behind a lip of the ovens case or housing while the opposite edge of the grille is secured to the housing by means of an Allen headed screw which is not readily visible or accessible. The run time meter itself is thereby also not visible or readily accessible and is connected in parallel with the primary winding of the power transformer for the magnetron tube, the electrical circuit for the oven being otherwise conventional. Hence the run time meter is activated only when the magnetron is energized and cumulatively records the periods of time during which that occurs.

.BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a front isometric view of a heavy duty, countertop microwave oven for use in restaurants and food vending installations, portions of the air inlet grille on the front of the oven being broken away to illustrate the location of the run time meter.

FIG. 2 is a partial sectional view taken along the line 22 of FIG. 1 illustrating the manner in which one edge of the grille is secured to the oven case.

FIG. 3 is a sectional view taken along the line 33 of FIG. 2 and illustrating the manner in which the other edge of the grille is secured to the oven case.

FIG. 4 is a schematic illustration of the electrical circuit of the oven illustrating the connection of the run time meter.

DESCRIPTION OF THE PREFERRED EMBODIMENT As shown in FIGS. 1-3, the microwave oven is contained in an outer rectangular case whose front is closed by a lower side-hinged door 11 and an upper outer louvered grille l2 and control panel 13. The door 1 l is opened by handle 14 for access to the oven cavity while the grille 12 provides an air inlet for cooling. The grille 12 itself is extruded from suitable material and carries an air filter 15 over its rear face retained by a pair of upper and lower flanges 16 formed integrally with the grille 12. Behind the latter and against the rear face of the filter 15 is an inner grille 17 which is permanently secured to the case 10 by means of vertical angle members 18a and 18b (see FIG. 2). The-grille 12 is removable and for this purpose one of its lateral edges 12a is retained behind a leg 19a of a decorative surround 19 about the front edges of the case 10. The opposite lateral edge 12b of the grille 12 is retained against the vertical angle member 18b by means of an Allen headed screw 20, threaded into the member 18b, which passes through a hat section bracket 21 secured to the rear face of the grille 12. A suitable Allen wrench 22 can engage the screw 20 through the louvres of the grille 12. Hence, by removing the screw 20, the edge 12b of the grille 12 can be swung out and the edge 12a released from behind the leg 19a to remove the grille 12 and filter l5 and expose the inner grille 17.

The electrical circuitry of the oven is largely conventional and well known so needs little description herein. Briefly, that circuit consists of a power line L connected to the blower motor BM and the primary windings of a power transformer T through the contacts of a power relay R1 and a surge suppressor relay R2, operation of the latter relay being controlled by the former. The relay R2 activates an indicator lamp I while the transformer T, of course, supplies power for the magnetron tube MT and its illustrated associated circuit. Relay R1 in turn is energized through a momentary start switch S1 and the contacts of a relay R3 and a dial timer DT, the latter also establishing a holding circuit for the relay R3 and activating the timer motor TM. A stop switch S2 opens the holding circuit to the relay R3, and thus the circuit through the dial timer DT to the timer motor MT and the relay R1 in order to halt operation of the oven at any time independently of the setting of the dial timer DT. Otherwise, at the end of a preset period the timer DT opens the circuits to its motor TM and the relays R1 and R3 and sounds a buzzer B. The switches S1 and S2, the dial timer DT and the indicator lamp 1, of course, are mounted on the control panel 13 as shown in FIG. 1. Safety is provided in the form of a pair of interlock switches S3 and S4 connected in series with the solenoids of the relays R1, R2 and R3 and controlled by the door 11 so that the oven cannot be operated unless and until the door 11 is fully closed. More than one safety interlock is used simply as a precautionary measure in case one should fail.

Across the primary windings of the transformer T in parallel with the power line L is connected an electrically driven run time meter RTM, of any suitable type, which visually and cumulatively records the total period of operation of the magnetron tube MT since the latter is operative only when the transformer T is energized. The RTM, as shown in FIGS. 1 and 2, extends through the lower right corner of the inner grille 17 and is concealed when the outer grille 12 is in place. Thus the RTM is accessible for reading only when the grille 12 is removed in the manner described above. In the case of rental ovens, to which the present invention is directed, this will normally be done only by an authorized serviceman or other representative of the lessor at which time the RTM can be read and the filter 15 cleaned or replaced.

Though the invention has been described in terms of a particular embodiment, it is not limited to that embodiment alone. Instead, the following claims are to be read as encompassing all adaptations and modifications of the invention falling within its spirit and scope.

I claim:

1. A microwave cooking oven comprising an electrical circuit including a power supply line and a magnetron power supply transformer with its primary winding connected to said supply line through switch means controlling energization power to said winding; electrically operated recording means connected in parallel with said primary windings, said recording means being energized only during the periods of time when said primary windings are energized, and cumulately and visually recording said periods; an outer housing enclosing said oven, a portion of the front of said housing being closed by a door for access to the cooking cavity of said oven, a control panel, and inner and outer grilles cover ing a second portion of said housing front, said grilles having an air filter sandwiched therebetween carried by said outer grille, said inner grille being permanently secured to said housing with said recording means located rearward of said inner grille and exposed therethrough for reading thereof, said recording means being normally covered by said outer grille and filter and normally visible and accessible for reading thereof only upon removal of said outer grille and filter; a lip disposed forward of said inner grille and engaging the forward face of said outer grille and filter along one edge thereof to secure said edge to said housing; releasable means securing an opposite edge of said outer grille and filter to said housing, said outer grille and filter being removable from said housing upon release of said releasable means, said releasable means being disposed rearward of said outer grille in a manner hiding the same from normal view through said outer grille and additionally requiring special means for release thereof. 

1. A microwave cooking oven comprising an electrical circuit including a power supply line and a magnetron power supply transformer with its primary winding connected to saiD supply line through switch means controlling energization power to said winding; electrically operated recording means connected in parallel with said primary windings, said recording means being energized only during the periods of time when said primary windings are energized, and cumulately and visually recording said periods; an outer housing enclosing said oven, a portion of the front of said housing being closed by a door for access to the cooking cavity of said oven, a control panel, and inner and outer grilles covering a second portion of said housing front, said grilles having an air filter sandwiched therebetween carried by said outer grille, said inner grille being permanently secured to said housing with said recording means located rearward of said inner grille and exposed therethrough for reading thereof, said recording means being normally covered by said outer grille and filter and normally visible and accessible for reading thereof only upon removal of said outer grille and filter; a lip disposed forward of said inner grille and engaging the forward face of said outer grille and filter along one edge thereof to secure said edge to said housing; releasable means securing an opposite edge of said outer grille and filter to said housing, said outer grille and filter being removable from said housing upon release of said releasable means, said releasable means being disposed rearward of said outer grille in a manner hiding the same from normal view through said outer grille and additionally requiring special means for release thereof. 